There are numerous applications for materials that can rapidly absorb and/or transfer fluids such as bodily wastes and the like. Examples include disposable personal care products such as disposable diapers and training pants, feminine hygiene products such as sanitary napkins and tampons, and incontinent care products such as pads and undergarments. Other industrial products such as wipers, oilsorb products and soakers have such requirements as do health care items such as bandages, for example. Because these fluids have different properties, it is difficult to provide a material adapted to fill many of these needs with an economy consistent with disposability that many such applications require. In particular, fluids such as menses, for example, have viscoelastic properties that challenge traditional absorption and distribution concepts. The viscosity and/or elastic components of such fluids tend to impose unique requirements for absorption and/or distribution. These requirements are often inconsistent with the best performance with respect to other components of the fluid that are less viscous or elastic with the result that a compromise in overall performance usually is required. For example, the pore and capillary sizes in an ideal material for absorbing and distributing less viscoelastic components are different from those that work best for the more viscoelastic components. Much effort has been expended to develop a material structure in nonwovens, foams, films and the like that meets all of these needs, but without complete success. Another approach is to modify the viscoelastic properties of the fluid itself. Numerous approaches have been employed to modify the bulk properties of viscoelastic fluids, including agents which affect intermolecular bonding and the physical entanglements of macromolecules.
Nonwoven fabrics and their manufacture have been the subject of extensive development resulting in a wide variety of materials for numerous applications. For example, nonwovens of light basis weight and open structure are used in personal care items such as disposable diapers as liner fabrics that provide dry skin contact but readily transmit fluids to more absorbent materials which may also be nonwovens of a different composition and/or structure. For many applications the ability to wick or transport viscous fluids such as menses is important for effective performance of these products by distributing the fluid to provide maximum use of absorbent properties of that or underlying materials. For other applications, nonwovens of heavier weights may be designed with pore structures making them suitable for filtration, absorbent and barrier applications such as wrappers for items to be sterilized, wipers or protective garments for medical, veterinary or industrial uses. Even heavier weight nonwovens have been developed for recreational, agricultural and construction uses. These are but a few of the practically limitless examples of types of nonwovens and their uses that will be known to those skilled in the art who will also recognize that new nonwovens and uses are constantly being identified. There have also been developed different ways and equipment to make nonwovens having desired structures and compositions suitable for these uses. Examples of such processes include spunbonding, meltblowing, carding, and others which will be described in greater detail below. The present invention has general applicability to nonwovens as will be apparent to one skilled in the art, and it is not to be limited by reference or examples relating to specific nonwovens which are merely illustrative.
It is not always possible to efficiently produce a nonwoven having all the desired properties as formed, and it is frequently necessary to treat the nonwoven to improve or alter properties such as wettability by one or more fluids, wicking or distribution properties, repellency to one or more fluids, electrostatic characteristics, conductivity, and softness, to name just a few examples. Conventional treatments involve steps such as dipping the nonwoven in a treatment bath, coating or spraying the nonwoven with the treatment composition, and printing the nonwoven with the treatment composition. For cost and other reasons it is usually desired to use the minimum amount of treatment composition that will produce the desired effect with an acceptable degree of uniformity. It is known, for example, that the heat of an additional drying step to remove water applied with the treatment composition can deleteriously affect strength properties of the nonwoven as well as add cost to the process. It is, therefore, desired to provide an improved treatment process and/or composition for nonwovens that can efficiently and effectively apply the desired treatment without adversely affecting desirable nonwoven web properties while also achieving the desired results. More particularly, it is desired to provide a treated nonwoven adapted for use with viscoelastic fluids and having the property of altering the characteristics such as viscosity and/or elasticity of a viscoelastic insult liquid so as to control fluid movement such as intake, distribution, and absorption, of the liquid in personal care product applications such as sanitary napkins.